Infections of the tendon sheath caused by non-tuberculous mycobacteria are well known. So far, only one case involving Mycobacterium malmoense has been reported. The authors report of a 73-year old patient having undergone carpal tunnel release. In spite of granulomatous inflammation of the flexor tendon sheaths, there was no biopsy cultured for acid-fast bacteria. One year later, symptoms recurred and synovialectomy was repeated. In spite of macroscopic appearance of the synovialis and histological studies, a specific diagnosis was not yet made. Two weeks later, acid-fast bacteria, identified as M. malmoense were cultured in the BACTEC vial. Because specific treatment was not initiated, a further recurrence developed five months later, necessitating further surgery with synovialectomy. Properly treated with Rifampin and Ethambutal for twelve months, the patient has remained asymptomatic for the following two years.